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<pre><span class="sourceLineNo">001</span>package org.slf4j;<a name="line.1"></a>
<span class="sourceLineNo">002</span><a name="line.2"></a>
<span class="sourceLineNo">003</span>import java.util.concurrent.BrokenBarrierException;<a name="line.3"></a>
<span class="sourceLineNo">004</span>import java.util.concurrent.CyclicBarrier;<a name="line.4"></a>
<span class="sourceLineNo">005</span><a name="line.5"></a>
<span class="sourceLineNo">006</span>/**<a name="line.6"></a>
<span class="sourceLineNo">007</span> * This class demonstrates that threads accessing the STATE variable always see a consistent value. <a name="line.7"></a>
<span class="sourceLineNo">008</span> * <a name="line.8"></a>
<span class="sourceLineNo">009</span> * During ongoing initialization the observed value is either ONGOING_INITIALIZATION<a name="line.9"></a>
<span class="sourceLineNo">010</span> * or one of {SUCCESS, FAILURE}. <a name="line.10"></a>
<span class="sourceLineNo">011</span> * <a name="line.11"></a>
<span class="sourceLineNo">012</span> * Post initialization the observed value is always one of  {SUCCESS, FAILURE}.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * <a name="line.13"></a>
<span class="sourceLineNo">014</span> * See also http://jira.qos.ch/browse/SLF4J-167 <a name="line.14"></a>
<span class="sourceLineNo">015</span> * <a name="line.15"></a>
<span class="sourceLineNo">016</span> * @author ceki<a name="line.16"></a>
<span class="sourceLineNo">017</span> *<a name="line.17"></a>
<span class="sourceLineNo">018</span> */<a name="line.18"></a>
<span class="sourceLineNo">019</span>public class DoubleCheckedInt {<a name="line.19"></a>
<span class="sourceLineNo">020</span><a name="line.20"></a>
<span class="sourceLineNo">021</span>    final static int THREAD_COUNT = 10 + Runtime.getRuntime().availableProcessors() * 2;<a name="line.21"></a>
<span class="sourceLineNo">022</span>    final static int UNINITIALIZED_STATE = 0;<a name="line.22"></a>
<span class="sourceLineNo">023</span>    final static int ONGOING_INITIALIZATION = 1;<a name="line.23"></a>
<span class="sourceLineNo">024</span>    final static int SUCCESS = 2;<a name="line.24"></a>
<span class="sourceLineNo">025</span>    final static int FAILURE = 3;<a name="line.25"></a>
<span class="sourceLineNo">026</span>    final static int NUMBER_OF_STATES = FAILURE + 1;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>    private static int STATE = UNINITIALIZED_STATE;<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>    public static int getState() {<a name="line.30"></a>
<span class="sourceLineNo">031</span>        if (STATE == 0) {<a name="line.31"></a>
<span class="sourceLineNo">032</span>            synchronized (DoubleCheckedInt.class) {<a name="line.32"></a>
<span class="sourceLineNo">033</span>                if (STATE == UNINITIALIZED_STATE) {<a name="line.33"></a>
<span class="sourceLineNo">034</span>                    STATE = ONGOING_INITIALIZATION;<a name="line.34"></a>
<span class="sourceLineNo">035</span>                    long r = System.nanoTime();<a name="line.35"></a>
<span class="sourceLineNo">036</span>                    try {<a name="line.36"></a>
<span class="sourceLineNo">037</span>                        Thread.sleep(10);<a name="line.37"></a>
<span class="sourceLineNo">038</span>                    } catch (InterruptedException e) {<a name="line.38"></a>
<span class="sourceLineNo">039</span>                    }<a name="line.39"></a>
<span class="sourceLineNo">040</span>                    if (r % 2 == 0) {<a name="line.40"></a>
<span class="sourceLineNo">041</span>                        STATE = SUCCESS;<a name="line.41"></a>
<span class="sourceLineNo">042</span>                    } else {<a name="line.42"></a>
<span class="sourceLineNo">043</span>                        STATE = FAILURE;<a name="line.43"></a>
<span class="sourceLineNo">044</span>                    }<a name="line.44"></a>
<span class="sourceLineNo">045</span>                }<a name="line.45"></a>
<span class="sourceLineNo">046</span>            }<a name="line.46"></a>
<span class="sourceLineNo">047</span>        }<a name="line.47"></a>
<span class="sourceLineNo">048</span>        return STATE;<a name="line.48"></a>
<span class="sourceLineNo">049</span>    }<a name="line.49"></a>
<span class="sourceLineNo">050</span><a name="line.50"></a>
<span class="sourceLineNo">051</span>    static public void main(String[] args) throws InterruptedException, BrokenBarrierException {<a name="line.51"></a>
<span class="sourceLineNo">052</span>        StateAccessingThread[] preInitializationThreads = harness();<a name="line.52"></a>
<span class="sourceLineNo">053</span>        check(preInitializationThreads, false);<a name="line.53"></a>
<span class="sourceLineNo">054</span><a name="line.54"></a>
<span class="sourceLineNo">055</span>        System.out.println("============");<a name="line.55"></a>
<span class="sourceLineNo">056</span>        StateAccessingThread[] postInitializationThreads = harness();<a name="line.56"></a>
<span class="sourceLineNo">057</span>        check(postInitializationThreads, true);<a name="line.57"></a>
<span class="sourceLineNo">058</span>    }<a name="line.58"></a>
<span class="sourceLineNo">059</span><a name="line.59"></a>
<span class="sourceLineNo">060</span>    private static StateAccessingThread[] harness() throws InterruptedException, BrokenBarrierException {<a name="line.60"></a>
<span class="sourceLineNo">061</span>        StateAccessingThread[] threads = new StateAccessingThread[THREAD_COUNT];<a name="line.61"></a>
<span class="sourceLineNo">062</span>        final CyclicBarrier barrier = new CyclicBarrier(THREAD_COUNT + 1);<a name="line.62"></a>
<span class="sourceLineNo">063</span>        for (int i = 0; i &lt; THREAD_COUNT; i++) {<a name="line.63"></a>
<span class="sourceLineNo">064</span>            threads[i] = new StateAccessingThread(barrier);<a name="line.64"></a>
<span class="sourceLineNo">065</span>            threads[i].start();<a name="line.65"></a>
<span class="sourceLineNo">066</span>        }<a name="line.66"></a>
<span class="sourceLineNo">067</span><a name="line.67"></a>
<span class="sourceLineNo">068</span>        barrier.await();<a name="line.68"></a>
<span class="sourceLineNo">069</span>        for (int i = 0; i &lt; THREAD_COUNT; i++) {<a name="line.69"></a>
<span class="sourceLineNo">070</span>            threads[i].join();<a name="line.70"></a>
<span class="sourceLineNo">071</span>        }<a name="line.71"></a>
<span class="sourceLineNo">072</span>        return threads;<a name="line.72"></a>
<span class="sourceLineNo">073</span>    }<a name="line.73"></a>
<span class="sourceLineNo">074</span><a name="line.74"></a>
<span class="sourceLineNo">075</span>    private static void check(StateAccessingThread[] threads, boolean postInit) {<a name="line.75"></a>
<span class="sourceLineNo">076</span><a name="line.76"></a>
<span class="sourceLineNo">077</span>        int[] stateCount = getStateCount(threads);<a name="line.77"></a>
<span class="sourceLineNo">078</span>        printStateCount(stateCount);<a name="line.78"></a>
<span class="sourceLineNo">079</span><a name="line.79"></a>
<span class="sourceLineNo">080</span>        if (stateCount[UNINITIALIZED_STATE] != 0) {<a name="line.80"></a>
<span class="sourceLineNo">081</span>            throw new IllegalStateException("getState() should never return a zero value");<a name="line.81"></a>
<span class="sourceLineNo">082</span>        }<a name="line.82"></a>
<span class="sourceLineNo">083</span><a name="line.83"></a>
<span class="sourceLineNo">084</span>        if (stateCount[SUCCESS] != 0 &amp;&amp; stateCount[FAILURE] != 0) {<a name="line.84"></a>
<span class="sourceLineNo">085</span>            throw new IllegalStateException("getState() should return consistent values");<a name="line.85"></a>
<span class="sourceLineNo">086</span>        }<a name="line.86"></a>
<span class="sourceLineNo">087</span><a name="line.87"></a>
<span class="sourceLineNo">088</span>        if (postInit) {<a name="line.88"></a>
<span class="sourceLineNo">089</span>            if (stateCount[SUCCESS] != THREAD_COUNT &amp;&amp; stateCount[FAILURE] != THREAD_COUNT) {<a name="line.89"></a>
<span class="sourceLineNo">090</span>                throw new IllegalStateException("getState() should return consistent values");<a name="line.90"></a>
<span class="sourceLineNo">091</span>            }<a name="line.91"></a>
<span class="sourceLineNo">092</span>        }<a name="line.92"></a>
<span class="sourceLineNo">093</span><a name="line.93"></a>
<span class="sourceLineNo">094</span>    }<a name="line.94"></a>
<span class="sourceLineNo">095</span><a name="line.95"></a>
<span class="sourceLineNo">096</span>    private static void printStateCount(int[] stateCount) {<a name="line.96"></a>
<span class="sourceLineNo">097</span>        for (int i = 0; i &lt; NUMBER_OF_STATES; i++) {<a name="line.97"></a>
<span class="sourceLineNo">098</span>            switch (i) {<a name="line.98"></a>
<span class="sourceLineNo">099</span>            case UNINITIALIZED_STATE:<a name="line.99"></a>
<span class="sourceLineNo">100</span>                System.out.println("UNINITIALIZED_STATE count: " + stateCount[i]);<a name="line.100"></a>
<span class="sourceLineNo">101</span>                break;<a name="line.101"></a>
<span class="sourceLineNo">102</span>            case ONGOING_INITIALIZATION:<a name="line.102"></a>
<span class="sourceLineNo">103</span>                System.out.println("ONGOING_INITIALIZATION count: " + stateCount[i]);<a name="line.103"></a>
<span class="sourceLineNo">104</span>                break;<a name="line.104"></a>
<span class="sourceLineNo">105</span>            case SUCCESS:<a name="line.105"></a>
<span class="sourceLineNo">106</span>                System.out.println("SUCCESS count: " + stateCount[i]);<a name="line.106"></a>
<span class="sourceLineNo">107</span>                break;<a name="line.107"></a>
<span class="sourceLineNo">108</span>            case FAILURE:<a name="line.108"></a>
<span class="sourceLineNo">109</span>                System.out.println("FAILURE count: " + stateCount[i]);<a name="line.109"></a>
<span class="sourceLineNo">110</span>                break;<a name="line.110"></a>
<span class="sourceLineNo">111</span>            }<a name="line.111"></a>
<span class="sourceLineNo">112</span>        }<a name="line.112"></a>
<span class="sourceLineNo">113</span>    }<a name="line.113"></a>
<span class="sourceLineNo">114</span><a name="line.114"></a>
<span class="sourceLineNo">115</span>    private static int[] getStateCount(StateAccessingThread[] threads) {<a name="line.115"></a>
<span class="sourceLineNo">116</span>        int[] valCount = new int[NUMBER_OF_STATES];<a name="line.116"></a>
<span class="sourceLineNo">117</span>        for (int i = 0; i &lt; threads.length; i++) {<a name="line.117"></a>
<span class="sourceLineNo">118</span>            int val = threads[i].state;<a name="line.118"></a>
<span class="sourceLineNo">119</span>            valCount[val] = valCount[val] + 1;<a name="line.119"></a>
<span class="sourceLineNo">120</span>        }<a name="line.120"></a>
<span class="sourceLineNo">121</span>        return valCount;<a name="line.121"></a>
<span class="sourceLineNo">122</span>    }<a name="line.122"></a>
<span class="sourceLineNo">123</span><a name="line.123"></a>
<span class="sourceLineNo">124</span>    static class StateAccessingThread extends Thread {<a name="line.124"></a>
<span class="sourceLineNo">125</span>        public int state = -1;<a name="line.125"></a>
<span class="sourceLineNo">126</span>        final CyclicBarrier barrier;<a name="line.126"></a>
<span class="sourceLineNo">127</span><a name="line.127"></a>
<span class="sourceLineNo">128</span>        StateAccessingThread(CyclicBarrier barrier) {<a name="line.128"></a>
<span class="sourceLineNo">129</span>            this.barrier = barrier;<a name="line.129"></a>
<span class="sourceLineNo">130</span>        }<a name="line.130"></a>
<span class="sourceLineNo">131</span><a name="line.131"></a>
<span class="sourceLineNo">132</span>        public void run() {<a name="line.132"></a>
<span class="sourceLineNo">133</span>            try {<a name="line.133"></a>
<span class="sourceLineNo">134</span>                barrier.await();<a name="line.134"></a>
<span class="sourceLineNo">135</span>            } catch (Exception e) {<a name="line.135"></a>
<span class="sourceLineNo">136</span>                e.printStackTrace();<a name="line.136"></a>
<span class="sourceLineNo">137</span>            }<a name="line.137"></a>
<span class="sourceLineNo">138</span>            state = DoubleCheckedInt.getState();<a name="line.138"></a>
<span class="sourceLineNo">139</span>        }<a name="line.139"></a>
<span class="sourceLineNo">140</span>    };<a name="line.140"></a>
<span class="sourceLineNo">141</span>}<a name="line.141"></a>




























































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